KR102552453B1 - Diamond Polycrystal and Tool with It - Google Patents

Abstract

In the Knoop hardness test conducted under the conditions specified in JIS Z 2251:2009, the first Knoop indentation formed on the surface of the polycrystal of diamond in a state where a Knoop indenter with a test load of 4.9 N is pressed into the surface of the polycrystal of diamond When the length of the longer diagonal is a and the length of the longer diagonal of the second Knoop indentation remaining on the surface of the diamond polycrystal after release of the test load is a', A diamond polycrystal having a ratio of a' (a'/a) of 0.99 or less.

Description

Diamond Polycrystal and Tool with It

The present disclosure relates to a diamond polycrystal and a tool having the same.

Diamond polycrystals have excellent hardness and have no directionality or cleavability of hardness, so they are widely used in tools such as cutting bites, dressers, dies, and excavating bits.

Conventional diamond polycrystals use diamond powder, which is a raw material, together with a sintering aid or binder under conditions of high pressure and high temperature (typically, a pressure of about 5 to 8 GPa and a temperature of about 1300 to 2200 ° C) in which diamond is thermodynamically stable. It is obtained by sintering in As a sintering aid, iron group element metals, such as Fe, Co, and Ni, carbonates, such as _CaCO3, etc. are used. As a binder, ceramics, such as SiC, etc. are used.

A sintering aid and a binder are contained in the diamond polycrystal obtained by the above method. Sintering aids and binders may cause deterioration in mechanical properties such as hardness and strength and heat resistance of the diamond polycrystal.

Diamond polycrystals obtained by removing the sintering aid in the diamond polycrystals by acid treatment, and diamond polycrystals with excellent heat resistance using heat-resistant SiC as a binder are also known. However, this diamond polycrystal has low hardness and strength, and its mechanical properties as a tool material are insufficient.

On the other hand, non-diamond carbon materials such as graphite, glassy carbon, amorphous carbon, and onion-like carbon are directly produced under ultra-high pressure and high temperature without using sintering aids or the like. It can be converted into diamonds. A diamond polycrystal is obtained by directly converting from a non-diamond phase to a diamond phase and simultaneously sintering it.

In Japanese Unexamined Patent Publication No. 2015-227278 (Patent Document 1), when the pressure is P (GPa) and the temperature is T (° C.) for non-diamond carbon powder, P≥0.0000168T2-0.0876T+124, T≤2300 , and, a technique for obtaining a diamond polycrystal by directly converting it into diamond under ultrahigh temperature and high pressure that satisfies the conditions of P≤25 is disclosed. In the obtained diamond polycrystal, in the measurement of Knoop hardness, the ratio (b/a) of the length a of the longer diagonal to the length b of the shorter diagonal of the Knoop indentation is 0.08 or less. and has elasticity.

In Japanese Unexamined Patent Publication No. 2018-008875 (Patent Document 2), onion-like carbon as a raw material is directly converted into diamond under ultra-high temperature and high pressure of 1200°C to 2300°C and 4 GPa to 25 GPa, and the Vickers hardness is 155 to 350 GPa, and a technique for obtaining ultra-hard nanotwinned diamond bulk material having a Knoop hardness of 140 to 240 GPa is disclosed.

[Patent Document 1] Japanese Unexamined Patent Publication No. 2015-227278 [Patent Document 2] Japanese Unexamined Patent Publication No. 2018-008875

[1] The diamond polycrystal of the present disclosure,

In the Knoop hardness test conducted under the conditions specified in JIS Z 2251:2009, the first Knoop indentation formed on the surface of the polycrystal of diamond in a state where a Knoop indenter with a test load of 4.9 N is pressed into the surface of the polycrystal of diamond When the length of the longer diagonal is a and the length of the longer diagonal of the second Knoop indentation remaining on the surface of the diamond polycrystal after release of the test load is a', A diamond polycrystal having a ratio of a' (a'/a) of 0.99 or less.

[2] The tool of the present disclosure is a tool provided with the diamond polycrystal of the above [1].

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining a Knoop indentation.

[Problems to be solved by the present disclosure]

The diamond polycrystal of Patent Literature 1 has high hardness and toughness, but further improvement in fracture resistance is required.

The ultra-hard nanotwinned diamond bulk material of Patent Document 2 had very high hardness, but had insufficient toughness and insufficient fracture resistance.

Accordingly, an object of the present invention is to provide a polycrystal of diamond having excellent fracture resistance while maintaining high hardness, and a tool provided therewith.

[Effect of the present disclosure]

According to the present disclosure, it becomes possible to provide a diamond polycrystal having excellent fracture resistance while maintaining high hardness, and a tool provided therewith.

[Description of Embodiments of the Present Disclosure]

Embodiments of the present disclosure are first opened and described.

(1) A diamond polycrystal according to an aspect of the present disclosure,

In the Knoop hardness test conducted under the conditions specified in JIS Z 2251:2009, the first Knoop indentation formed on the surface of the polycrystal of diamond in a state where a Knoop indenter with a test load of 4.9 N is pressed into the surface of the polycrystal of diamond When the length of the longer diagonal is a and the length of the longer diagonal of the second Knoop indentation remaining on the surface of the diamond polycrystal after release of the test load is a', A diamond polycrystal having a ratio of a' (a'/a) of 0.99 or less.

This diamond polycrystal has excellent fracture resistance while maintaining high hardness.

(2) The polycrystal of the diamond preferably has a Knoop hardness calculated from the value of a of 100 GPa or more and less than 140 GPa. This diamond polycrystal has high hardness and excellent wear resistance.

(3) The polycrystal of the diamond preferably has a Knoop hardness calculated from the value of a of 120 GPa or more and less than 140 GPa. Since this diamond polycrystal has high hardness, it is further excellent in wear resistance.

(4) the diamond polycrystal is composed of a plurality of diamond grains;

It is preferable that the said diamond particle has an average particle diameter of 100 nm or less.

According to this, the diamond polycrystal can be suitably applied to tools for applications requiring tough and high-precision cutting edges, such as high-load machining and micromachining.

(5) A tool according to one aspect of the present disclosure is a tool provided with the diamond polycrystal described in any one of (1) to (4) above.

This tool has excellent fracture resistance in processing various materials.

[Details of Embodiments of the Present Disclosure]

A specific example of a polycrystal of diamond and a tool using the polycrystal of diamond according to an embodiment of the present disclosure will be described below with reference to the drawings.

In this specification, the notation in the form of "A to B" means the lower limit and upper limit of the range (ie, from A to B), and when no unit is described in A and a unit is described only in B, A Units and units of B are the same.

[Diamond Polycrystal]

The diamond polycrystal according to the present embodiment has diamond as a basic composition. That is, the diamond polycrystal has diamond as its basic composition and substantially does not contain a bonding phase (binder) formed by one or both of the sintering aid and the binder. Therefore, it has very high hardness and strength, and even under high-temperature conditions, deterioration of mechanical properties due to the difference in thermal expansion coefficient with the binder or the catalytic action of the binder does not occur.

Since the diamond polycrystal is a polycrystal composed of a plurality of diamond grains, it does not have anisotropy and cleavage like single crystals, and has isotropic hardness and wear resistance in all directions.

The diamond polycrystal of the present disclosure has an integrated intensity greater than 10% of the total integrated intensity of all diffraction peaks derived from the diamond structure in an X-ray diffraction spectrum obtained by an X-ray diffraction method, other than a diamond structure. It is defined that no diffraction peaks originating from are present. That is, it can be confirmed from the X-ray diffraction spectrum that the diamond polycrystal does not contain the above bonding phase. The integrated intensity of the diffraction peak is the value excluding the background. An X-ray diffraction spectrum can be obtained by the method described below.

The diamond polycrystal is ground with a diamond grindstone, and the processed surface is used as an observation surface.

An X-ray diffraction spectrum of a processed surface of a diamond polycrystal is obtained using an X-ray diffractometer ("MiniFlex600" (trade name) manufactured by Rigaku). The conditions of the X-ray diffractometer at this time are, for example, as follows.

Characteristic X-rays: Cu-Kα (wavelength 1.54 Å)

Tube voltage: 45 kV

Tube current: 40 mA

Filter: Multilayer Mirror

Optics: concentrating method

X-ray diffraction method: θ-2θ method.

The diamond polycrystal may contain unavoidable impurities as long as the effect of the present embodiment is exhibited. As an unavoidable impurity, hydrogen of 1 ppm or less, oxygen of 1 ppm or less, nitrogen of 1 ppm or less, etc. are mentioned, for example. The concentration of an unavoidable impurity in the present specification means a concentration based on the number of atoms.

The respective concentrations of hydrogen, oxygen, and nitrogen in the diamond polycrystal are preferably 1 ppm or less, more preferably 0.1 ppm or less, from the viewpoint of improving the strength. The total impurity concentration in the diamond polycrystal is preferably 3 ppm or less, more preferably 0.3 ppm or less. The lower limit of each concentration of hydrogen, oxygen and nitrogen in the diamond polycrystal is not particularly limited, but is preferably 0.001 ppm or more from the viewpoint of production.

The concentrations of hydrogen, oxygen, and nitrogen in the diamond polycrystal can be measured by secondary ion mass spectrometry (SIMS).

The polycrystal of diamond in this embodiment is a sintered body, but since a sintered body is often intended to contain a binder, the term “polycrystal” is used in this embodiment.

(diamond particle)

It is preferable that the diamond particle has an average particle diameter of 100 nm or less. Diamond polycrystals composed of diamond particles having such a small average grain size can be suitably applied to tools for applications requiring tough and high-precision cutting edges, such as high-load machining and micro-machining. If the average particle diameter of the diamond particles exceeds 100 nm, the precision of the edge deteriorates, and chipping of the edge easily occurs, and it cannot be applied to a tool for precise processing under high load.

From the viewpoint of suitably applying diamond polycrystals to tools for applications requiring tough and highly accurate cutting edges, the average particle diameter of diamond particles is more preferably 50 nm or less, and more preferably 20 nm or less. From this point of view, the average particle diameter of the diamond particles can be 15 nm or less, and can also be 10 nm or less.

From the viewpoint of obtaining the mechanical strength peculiar to diamond, the lower limit of the average particle diameter of diamond particles is preferably 1 nm or more. From this point of view, the average particle diameter of the diamond particles can be 10 nm or more, and can also be 15 nm or more.

The average particle diameter of the diamond particles is preferably 1 nm or more and 100 nm or less, more preferably 10 nm or more and 60 nm or less, and still more preferably 15 nm or more and 50 nm or less.

The average particle diameter of a diamond particle can be obtained by image observation of a surface obtained by polishing a diamond polycrystal to a flat mirror surface using a scanning electron microscope (SEM). The specific method is as follows.

The surface of the diamond polycrystal, which has been polished to a flat mirror surface by polishing with a diamond wheel or the like, is observed using a high-resolution scanning electron microscope at a magnification of 1000 to 100000 to obtain an SEM image. As a high-resolution scanning electron microscope, it is preferable to use, for example, a field emission scanning electron microscope (FE-SEM).

Next, a circle is drawn on the SEM image, and eight straight lines are radially drawn from the center of the circle to the outer circumference of the circle (so that the intersection angles between the straight lines are substantially equal). In this case, it is preferable to set the above-mentioned observation magnification and circle diameter so that the number of diamond grains (crystal grains) lying on one straight line described above is about 10 to 50.

Next, count the number of lines crossing the grain boundaries of the diamond grains for each straight line, divide the length of the straight line by the number of lines crossing it to obtain the average intercept length, and multiply the average intercept length by 1.128 to obtain the value obtained as the average particle diameter. . Using three SEM images, the average particle diameter is obtained for each image in the same manner as described above, and the average value of the average particle diameters of the three images is set as "average particle diameter of diamond particles".

The aspect ratio (A/B) of the major axis A and the minor axis B of the diamond particles in the SEM image is preferably 1≤A/B<4 from the viewpoint of suppressing the occurrence of microcracks. Here, the major axis means the distance between the two most distant points on the outline of the diamond particle. The minor axis means the distance of a straight line that is orthogonal to the straight line defining the major axis and has the longest distance between the intersections of two points with the outer edge of the diamond particle.

(Knoop Hardness)

The diamond polycrystal of the present embodiment is subjected to a Knoop hardness test conducted under the conditions specified in JIS Z 2251:2009, in a state where a Knoop indenter with a test load of 4.9 N is pressed into the surface of the diamond polycrystal. When the length of the long diagonal of the first Knoop indentation formed in is a and the length of the long diagonal of the second Knoop indentation remaining on the surface of the diamond polycrystal after release of the test load is a' , the ratio of a' to a (a'/a) is 0.99 or less.

The Knoop hardness test specified in JIS Z 2251:2009 is known as one of the methods for measuring the hardness of industrial materials. The Knoop hardness test is to determine the hardness of a material to be measured by pressing a Knoop indenter against the material to be measured at a predetermined temperature and with a predetermined load (test load). In this embodiment, the predetermined temperature is 23° C.±5° C., and the predetermined load is 4.9 N.

A Knoop indenter refers to an indenter made of diamond having the shape of a quadrangular pyramid with a rhombic bottom surface. In the Knoop hardness test, the apex side opposite to the bottom surface of the Knoop indenter is pressed into the material to be measured. In the present specification, a Knoop indentation is a rhombic shape formed on the surface of a material to be measured (diamond polycrystal in this embodiment) in a state in which a Knoop indenter is pressed into the surface of the material to be measured at a predetermined temperature and a predetermined test load. First Knoop indentation (refer to “First Knoop indentation” in FIG. 1), which is a trace, and second Knoop indentation (“Second Knoop indentation” in FIG. Knoop indentation” reference) is defined as a meaning including.

In a perfectly sintered body such as a normal metal material, the first Knoop indentation in the state where the Knoop indenter is pushed in and the second Knoop indentation remaining after the Knoop indenter is removed have the same shape. The Knoop indentation takes on the same shape before and after release of the test load, and becomes, for example, a diamond shape indicated by a broken line as a “first Knoop indentation” in FIG. 1 . Therefore, in the perfectly sintered body, the above a and the above a' are the same (a = a'). Further, the length b of the shorter diagonal of the first Knoop indentation (see Fig. 1) and the length of the shorter diagonal of the second Knoop indentation b' (see Fig. 1) are also the same (b = b').

On the other hand, when the material to be measured is an elastic material, when the test load is released by removing the indenter, the Knoop indentation undergoes elastic recovery in the direction of the arrow indicating the elastic recovery in Fig. 1, and the Knoop indentation tries to return to its original state, resulting in permanent deformation. reaching the trace (elastic recovery). In this case, the a and a' represent a relationship of a>a', and the b and b' represent a relationship of b>b'.

When the return in the direction of the arrow indicating the elastic recovery in FIG. 1 is increased, the value of the ratio of a' to a (a'/a) and the ratio of b' to b (b'/b) value gets smaller That is, the value of the ratio (a'/a) and the smaller the value of the ratio (b'/b) indicate that the elastic recovery (elastic property) is greater.

Elastic recovery occurs more easily in the direction along the shorter diagonal line of the Knoop indentation (elastic recovery from b to b') than in the direction along the longer diagonal line of the Knoop indentation (elastic recovery from a to a').

Since the elasticity of conventional general diamond polycrystals is very small, a and a' are the same length (a=a'), and b and b' are also the same length (b=b').

Since the diamond polycrystal of Patent Literature 1 has elasticity, the above b and the above b' show a relationship of b > b'. However, since the elasticity is small, the values of a and a' are almost equal (a≒a').

On the other hand, the diamond polycrystal of the present embodiment has a ratio of a' to a (a'/a) of 0.99 or less, and has greater elasticity than that of the diamond polycrystal of Patent Literature 1. Since the diamond polycrystal of the present embodiment has high elasticity, resistance to cracking against tensile stress is improved. For this reason, when diamond polycrystal is used as a material for a tool, stress concentration applied to the edge is alleviated and damage due to chipping of the edge is suppressed.

In addition, since the edge of the diamond polycrystal of the present embodiment is elastically deformed when used for cutting that requires ultra-precision, diffraction phenomena (so-called iridescent patterns) due to cutting marks, which are a problem in mirror processing, etc. ) becomes difficult to occur.

In the diamond polycrystal according to the present embodiment, the value of the ratio (a'/a) of a' to a is 0.99 or less. When the value of the ratio (a'/a) exceeds 0.99, brittleness increases and cracks tend to occur when a local stress is applied.

0.98 or less is preferable and, as for the value of the said ratio (a'/a), 0.9 or less is more preferable. The smaller the value of the ratio (a'/a), the greater the elastic deformability. If the elastic deformability is too large, when used as a tool, workability may be deteriorated due to deformation of the edge during processing. From this point of view, the value of the ratio (a'/a) is preferably 0.7 or more. The value of the ratio (a'/a) is preferably 0.7 or more and 0.99 or less, more preferably 0.7 or more and 0.98 or less, and still more preferably 0.7 or more and 0.9 or less.

In the present specification, the length a of the long diagonal line and the length b of the short diagonal line in the first Knoop indentation, and the length a' of the long diagonal line and the length of the short diagonal line in the second Knoop indentation. The length b' of is measured by the following method.

In the Knoop hardness test conducted under the conditions specified in JIS Z 2251:2009, a Knoop indenter with a test load of 4.9 N is pressed into the surface of a diamond polycrystal. Thereafter, after releasing the test load, the permanently deformed second Knoop indentation formed on the surface of the diamond polycrystal is observed with an optical microscope equipped with a conventional micro hardness tester or with a laser microscope to observe the second Knoop indentation. Measure the length a' of the longer diagonal and the length b' of the shorter diagonal in .

In addition, the surface of the diamond polycrystal after release of the test load was examined using a high-resolution scanning electron microscope (e.g., a field emission scanning electron microscope (FE-SEM)) or a high-sensitivity differential interference microscope (providing contrast of interference colors by polarization interference). and observe it precisely with a microscope).

When the surface of the diamond polycrystal is observed with a high-resolution scanning electron microscope or a high-sensitivity differential interference microscope, as shown in FIG. Very slight streak indentations not observed under a microscope are observed.

The length a' of the longer diagonal line in the second Knoop indentation, and the lengths a'1 and a'2 of stripe indentations continuing with the ends of the longer diagonal line are measured. The length of the longer diagonal a' and the sum of the lengths a'1 and a'2 of the stripe indentation (a'+a'1+a'2) are the lengths of the longer diagonal in the first Knoop indentation a do it with

The length b' of the shorter diagonal line in the second Knoop indentation and the lengths b'1 and b'2 of the stripe indentations continuing with the ends of the shorter diagonal line are measured. The length of the shorter diagonal in the first Knoop indentation b' and the sum of the lengths b'1 and b'2 of the stripe indentation (b'+b'1+b'2) do it with

The diamond polycrystal of the present embodiment preferably has a Knoop hardness calculated from the value a above of 100 GPa or more and less than 140 GPa. This diamond polycrystal has high hardness and can have excellent wear resistance. When the Knoop hardness is less than 100 GPa, for example, when a cutting tool is manufactured using a diamond polycrystal, the wear of the edge of the blade increases and it may not be usable. On the other hand, when the Knoop hardness is 140 GPa or more, for example, when a cutting tool is manufactured using a diamond polycrystal, the edge may be easily chipped. The Knoop hardness is more preferably 120 GPa or more and less than 140 GPa, and still more preferably 130 GPa or more and less than 140 GPa, from the viewpoint of improving wear resistance.

In this specification, the Knoop hardness is a value obtained by the following method based on the first Knoop indentation. First, the length a (μm) of the longer diagonal of the first Knoop indentation is measured. Since the measurement method of the length a of the longer diagonal of the first Knoop indentation is as described above, the description thereof will not be repeated. The Knoop hardness (HK) is calculated from the following formula (1) using the value of the length a of the longer diagonal.

HK=14229×F/a ² Equation (1)

Further, when the Knoop hardness is calculated based on a' in the second Knoop indentation, this Knoop hardness becomes the apparent hardness after elastic recovery and is larger than the original Knoop hardness value based on the first Knoop indentation. This apparent hardness does not represent the exact hardness of an industrial material on the premise that indentation of permanent deformation, which is specified in JIS Z 2251:2009, is formed.

[tool]

Since the diamond polycrystal of the present embodiment has high hardness, high elasticity, and excellent fracture resistance, it can be suitably used for cutting tools, wear-resistant tools, grinding tools, tools for friction stir welding, and the like. That is, the tool of this embodiment is equipped with the above-described diamond polycrystal.

The tool may be entirely composed of polycrystal diamond, or only a part thereof (for example, the edge of a cutting tool in the case of a cutting tool) may be composed of polycrystal diamond. In addition, each tool may have a coating film formed on its surface.

As cutting tools, drills, end mills, interchangeable blade cutting tips for drills, exchangeable blade cutting tips for end mills, exchangeable blade cutting tips for flea processing, exchangeable blade tip cutting tips for turning, metal saws, gear cutting tools, reamers, A tap, a cutting bite, etc. are mentioned.

Examples of wear-resistant tools include dies, scribers, scribing wheels, and dressers.

As a grinding tool, a grinding grindstone etc. are mentioned.

[Method for producing diamond polycrystal]

The diamond polycrystal described above can be produced, for example, by the following method.

First, a non-diamond-like carbon material having a graphitization degree of 0.4 or less is prepared. The non-diamond-like carbon material is not particularly limited as long as it has a graphitization degree of 0.4 or less and is a non-diamond carbon material.

For example, when a non-diamond-like carbon material is produced by thermal decomposition from a high-purity gas, a non-diamond-like carbon material having a graphitization degree of 0.4 or less and a concentration of impurities such as hydrogen, oxygen, and nitrogen of 1 ppm or less can be obtained. there is.

Non-diamond carbon materials are not limited to those produced by the pyrolysis method from high purity gas. For example, it may be finely pulverized graphite in a high-purity inert gas atmosphere, graphite with a low degree of graphitization such as high-purity refining amorphous carbon, amorphous carbon material, or a mixture thereof.

The degree of graphitization (P) of the non-diamond-like carbon material can be determined as follows. The interplanar spacing (d 002 ) of the ( ₀₀₂ ) plane of the graphite of the non-diamond-like carbon material was measured by X-ray diffraction of the non-diamond-like carbon material, and by the following equation (2),

d ₀₀₂ =3.440-0.086×(1-p ² ) Equation (2)

The ratio p of the random-layered structure portion of the non-diamond-like carbon material is calculated. From the ratio (p) of the turbostratic structure obtained in this way, by the following equation (3),

P=1-p Equation (3)

The degree of graphitization (P) is calculated.

It is preferable that the non-diamond-like carbon material does not contain an impurity iron group element metal from the viewpoint of suppressing the growth of crystal grains.

The non-diamond-like carbon material preferably has a low concentration of impurities such as hydrogen, oxygen, and nitrogen from the viewpoint of suppressing crystal grain growth and promoting direct conversion into diamond. The concentration of hydrogen, oxygen and nitrogen in the non-diamond-like carbon material is preferably 1 ppm or less, more preferably 0.1 ppm or less, respectively. Further, the total impurity concentration in the non-diamond-like carbon material is preferably 3 ppm or less, more preferably 0.3 ppm or less. In this specification, the concentration of impurities means the concentration based on the number of atoms.

The concentration of impurities such as hydrogen, oxygen, and nitrogen in the non-diamond-like carbon raw material can be measured by secondary ion mass spectrometry (SIMS).

Next, for the above non-diamond-like carbon material, when the pressure is P (GPa) and the temperature is T (°C), P and T are simultaneously increased under the conditions that satisfy T≤1000 °C and P≤10 GPa. and raise the temperature to a pressure and temperature that satisfy P≥0.0000903T ² -0.394T+443 and P≤0.000148T ² -0.693T+823, and hold at the pressure and temperature reached by the pressure and temperature for 1 minute or longer By holding, a diamond polycrystal is obtained.

If the temperature is higher than the temperature that satisfies the above conditions, the grain size of the diamond particles coarsens regardless of the pressure, and there is a risk that a high-strength diamond polycrystal cannot be obtained. On the other hand, if the temperature is lower than the temperature that satisfies the above conditions, there is a possibility that the sinterability is lowered and the bonding force between the diamond particles is lowered regardless of the pressure. The sintering time at the pressure and temperature described above is preferably 5 minutes to 20 minutes, and more preferably 10 minutes to 20 minutes.

The high-pressure and high-temperature generator used in the diamond polycrystal production method of the present embodiment is not particularly limited as long as the pressure and temperature conditions of the diamond phase are thermodynamically stable, but from the viewpoint of improving productivity and workability, A belt type or multi-anvil type is preferred. Further, the container for storing the non-diamond-like carbon material as a raw material is not particularly limited as long as it is a material with high pressure resistance and high temperature resistance, and for example, Ta, Nb, or the like is suitably used.

In order to prevent the incorporation of impurities into the diamond polycrystal, for example, a non-diamond-like carbon material as a raw material is placed in a capsule made of a high-melting point metal such as Ta or Nb, heated in vacuum and sealed, and adsorbed gas from the non-diamond-like carbon material. or air is removed, and the above pressure and temperature (when the pressure is P(GPa) and the temperature is T(℃), under the conditions that satisfy T≤1000℃ and P≤10 GPa, P and T simultaneously increase the pressure) It is preferable to convert directly into diamond under ultra-high pressure and high temperature (pressure and temperature that satisfy P≥0.0000903T ² -0.394T+443, and P≤0.000148T ² -0.693T+823) reached by heating.

Example

The present embodiment will be described more specifically by examples. However, this embodiment is not limited by these examples.

[Production Example 1 to Production Example 11]

(Production of diamond polycrystal)

First, a raw material for a diamond polycrystal is prepared. In Production Examples 1 to 4 and Production Examples 8 to 11, non-diamond-like carbon materials having the degree of graphitization shown in Table 1 are prepared. In Production Example 5 and Production Example 6, conventional isotropic graphite prepared by firing graphite powder is prepared. In Production Example 7, graphite having a low degree of graphitization and containing about 0.1% by mass of impurities (hydrogen and oxygen) was pulverized with a planetary ball mill to an average particle diameter of 8 nm to prepare a powder.

Next, in Production Examples 1 to 10, the raw material prepared above was placed in a capsule made of Ta, heated in a vacuum, sealed, and pressurized to a pressure of 8 GPa using a high-pressure, high-temperature generator, and then to a temperature of 300 ° C. The diamond polycrystal is obtained by heating and then simultaneously raising the pressure and temperature to a pressure of 16 GPa and a temperature of 2170° C., and performing a high-pressure and high-temperature treatment for 15 minutes under these pressure and temperature conditions. In addition, neither a sintering aid nor a binder is added to the raw material.

In Production Example 11, the raw material prepared above was placed in a capsule made of Ta, heated in a vacuum, sealed, and pressurized to a pressure of 16 GPa using a high-pressure, high-temperature generator, and then heated to a temperature of 2170 ° C. Diamond polycrystals are obtained by high-pressure and high-temperature treatment for 15 minutes under conditions. In addition, neither a sintering aid nor a binder is added to the raw material.

For the obtained diamond polycrystal, the average particle diameter of the diamond particle, the X-ray diffraction spectrum, the impurity concentration, the length a of the long diagonal line of the first Knoop indentation, the length a' of the long side diagonal line of the second Knoop indentation, Knoop hardness , and, the crack initiation load is measured.

(average particle diameter of diamond particles)

The average particle diameter of diamond particles contained in each diamond polycrystal is determined by a cutting method using a scanning electron microscope (SEM). The specific method is as follows.

First, a polished diamond polycrystal is observed using a field emission scanning electron microscope (FE-SEM) to obtain an SEM image.

Next, a circle is drawn on the SEM image, and eight straight lines are drawn from the center of the circle radially (so that the intersection angles between the straight lines are substantially equal) to the outer circumference of the circle. In this case, the above observation magnification and the diameter of the circle are set so that the number of diamond grains placed per one straight line described above is about 10 to 50.

Subsequently, the number of crossings of the grain boundaries of the diamond grains is counted for each straight line, the average intercept length is obtained by dividing the length of the straight line by the number of crossings, and the average intercept length is multiplied by 1.128, and the obtained value is the average particle diameter. .

Incidentally, the magnification of the SEM image described above is set to 30000 times. The reason for this is that at a magnification lower than this, the number of particles in the circle increases, grain boundaries become difficult to see, measurement errors occur, and the possibility of including plate-like structures when drawing lines increases. Also, at a magnification exceeding this, the number of particles in the circle is too small, and an accurate average particle diameter cannot be calculated.

For each production example, three SEM images of one sample taken at different locations are used, and the average particle diameter is obtained for each SEM image by the method described above, and the average of the three obtained average particle diameters is taken as the average particle diameter. The results are shown in the "average particle diameter of diamond particles" column of Table 1.

(X-ray diffraction spectrum)

An X-ray diffraction spectrum of the obtained diamond polycrystal is obtained by an X-ray diffraction method. Since the specific method of the X-ray diffraction method is as described in the mode for carrying out the invention described above, the description thereof will not be repeated. In the X-ray diffraction spectra of the diamond polycrystals of all production examples, it was confirmed that there was no diffraction peak derived from anything other than the diamond structure having an integrated intensity greater than 10% of the sum of the integrated intensities of all diffraction peaks derived from the diamond structure. do.

(impurity concentration)

Using SIMS, each concentration of nitrogen (N), hydrogen (H), and oxygen (O) in the diamond polycrystal is measured.

In the diamond polycrystals of Production Examples 1 to 6 and Production Examples 8 to 11, the total amount of nitrogen, hydrogen, and oxygen is 3 ppm or less. Production Example 7 contains hydrogen and oxygen on the order of 1000 ppm, respectively.

(Length a of the long side diagonal of the first Knoop indentation, length a' of the long side diagonal of the second Knoop indentation)

In the Knoop hardness test conducted under the conditions specified in JIS Z 2251:2009, a Knoop indenter with a test load of 4.9 N is pressed into the surface of a diamond polycrystal. Pressing of the Knoop indenter is performed for 10 seconds. Then, after releasing the test load, by observing the permanently deformed second Knoop indentation formed on the surface of the diamond polycrystal with an optical microscope equipped with an ordinary micro hardness tester, the length of the second Knoop indentation in the second Knoop indentation The diagonal length a' (hereinafter also referred to as "a'") is measured.

Further, the surface of the diamond polycrystal after releasing the test load was observed with a field emission scanning electron microscope (FE-SEM), and the length a of the long diagonal of the first Knoop indentation (hereinafter also referred to as "a") ) is measured.

(Knoop Hardness)

From the value of the length a (micrometer) of the long side diagonal of a 1st Knoop indentation, the Knoop hardness (HK) is computed by following Formula (4).

HK=14229×4.9/a ² Equation (4)

The results are shown in the "a", "a'" and "Knoop hardness" columns of Table 1. Further, based on the values of "a" and "a'", the value of "a'/a" is calculated. The results are shown in the "a'/a" column of Table 1.

(crack initiation load)

For the diamond polycrystal, a fracture strength test is conducted under the following conditions in order to measure the crack generation load.

A spherical diamond indenter with a tip radius of R50 μm was prepared, and a load was applied to each sample at a load rate of 1 N/sec at room temperature (23° C.±5° C.), and the load at the moment when the sample cracked (crack generation load ) is measured. The moment at which cracks occur is measured with an AE sensor. This measurement is made 5 times. The crack generation load of each sample is taken as the average value of 5 values of the results of 5 measurements. The results are shown in the "crack generation load" column of Table 1. The higher the crack generation load, the higher the strength of the sample and the better the fracture resistance.

(Mirror cutting process test)

In order to investigate the fracture resistance of the tool provided with the diamond polycrystal of each manufacturing example, a ball end mill tool with a diameter of 0.5 mm was manufactured using the diamond polycrystal, and the cemented carbide (WC-12% Co, particle size 0.3 μm) A mirror cutting process is performed on the end face. Specific cutting conditions are as follows.

Rotation speed: 36,000 rpm, cutting speed: 120 mm/min, machining length: 5 μm, cutting width: 1 μm, machining time: 3.5 hr, machining area: 4×5 mm.

After cutting, observe the state of the blade edge of the tool and check the presence or absence of edge chipping. Here, “presence” of edge chipping means a state in which a concave portion having a width of 0.1 μm or more or a depth of 0.01 μm or more has occurred. The results are shown in the "Edge Chipping" column of "Mirror Cutting Test" in Table 1.

After cutting, observe the state of the edge of the tool and measure the amount of wear on the edge. Here, the amount of wear “small” means that the amount of wear is 0 μm or more and less than or equal to 5 μm, the amount of wear “medium” means that the amount of wear exceeds 5 μm and less than or equal to 20 μm, and the amount of wear “large” means that the amount of wear exceeds 20 μm it means. The results are shown in the "abrasion amount" column of "mirror cutting test" in Table 1.

After cutting, the surface roughness (Ra) of the machined surface of the cemented carbide as a work material is measured with a laser microscope. The smaller the value of the surface roughness (Ra), the better the machined surface. The results are shown in the "Machined Surface Roughness (Ra)" column of the "Mirror Cutting Test" in Table 1.

(Review)

The diamond polycrystals of Production Examples 1 to 4 and Production Examples 8 to 10 have a ratio (a'/a) value of 0.99 or less, and correspond to examples. The diamond polycrystals of Production Examples 5 to 7 and Production Example 11 have a ratio (a'/a) of more than 0.99 and correspond to comparative examples.

It has been confirmed that the diamond polycrystals of Production Examples 1 to 4 have high hardness, have a high crack generation load, high strength, and excellent fracture resistance compared to Production Examples 5 to 7 and Production Example 11. do. It is confirmed that the tools of Production Examples 1 to 4 do not generate edge chipping in the mirror cutting test, have a small amount of wear, and are excellent in fracture resistance and wear resistance. In addition, according to the tools of Production Examples 1 to 4, in the mirror cutting test, the surface roughness of the machined surface of the workpiece was small, and it was confirmed that the machined surface was good.

It was confirmed that the diamond polycrystals of Production Examples 5, 6, and 11 had high hardness, but had a lower crack generation load than Production Examples 1 to 4, and were inferior in fracture resistance. Further, in the tools of Production Example 5, Production Example 6, and Production Example 11, edge chipping occurred in the mirror cutting test, and it was confirmed that the fracture resistance was inferior.

It was confirmed that the diamond polycrystal of Production Example 7 had insufficient hardness, and also had a small crack generation load, and was inferior in fracture resistance. Further, in the tool of Production Example 7, edge chipping occurred in the mirror cutting test, and it was confirmed that the fracture resistance was inferior.

It is confirmed that the diamond polycrystal of Production Example 8 has high hardness, has a large crack generation load, high strength, and excellent fracture resistance compared to Production Examples 5 to 7 and Production Example 11. In the tool of Production Example 8, it was confirmed that edge chipping did not occur in the mirror cutting test, the amount of wear was moderate, and the fracture resistance and wear resistance were excellent. In addition, according to the tool of Production Example 8, in the mirror cutting test, the surface roughness of the machined surface of the workpiece was small, and it was confirmed that the machined surface was good.

It is confirmed that the diamond polycrystal of Production Example 9 has high hardness, has a large crack generation load, high strength, and excellent fracture resistance compared to Production Examples 5 to 7 and Production Example 11. In the tool of Production Example 9, it was confirmed that edge chipping did not occur in the mirror cutting test, the amount of wear was moderate, and the fracture resistance and wear resistance were excellent. In addition, according to the tool of Production Example 9, in the mirror cutting test, the surface roughness of the machined surface of the workpiece was small, and it was confirmed that the machined surface was good.

It is confirmed that the diamond polycrystal of Production Example 10 has high hardness, has a large crack generation load, high strength, and excellent fracture resistance compared to Production Examples 5 to 7 and Production Example 11. In the tool of Production Example 10, it was confirmed that edge chipping did not occur in the mirror cutting test, the amount of wear was moderate, and the fracture resistance and wear resistance were excellent.

As described above, the embodiments and examples of the present invention have been described, but it is also planned from the beginning to appropriately combine or modify the configuration of each of the above-described embodiments and examples.

It should be considered that the embodiments and examples disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims rather than the above-described embodiments and examples, and it is intended that the meaning equivalent to the claims and all changes within the scope are included.

Claims (5)

In the Knoop hardness test conducted under the conditions specified in JIS Z 2251:2009, the first Knoop indentation formed on the surface of the polycrystal of diamond in a state where a Knoop indenter with a test load of 4.9 N is pressed into the surface of the polycrystal of diamond When the length of the longer diagonal is a and the length of the longer diagonal of the second Knoop indentation remaining on the surface of the diamond polycrystal after release of the test load is a', A diamond polycrystal having a ratio of a' (a'/a) of 0.99 or less. The polycrystal of diamond according to claim 1, wherein the polycrystal of diamond has a Knoop hardness calculated from the value of a of 100 GPa or more and less than 140 GPa. The polycrystal of diamond according to claim 2, wherein the polycrystal of diamond has a Knoop hardness calculated from the value of a of 120 GPa or more and less than 140 GPa. The method according to any one of claims 1 to 3, wherein the diamond polycrystal is composed of a plurality of diamond grains,
The diamond particle is a diamond polycrystal having an average particle diameter of 100 nm or less. A tool comprising the diamond polycrystal according to any one of claims 1 to 3.

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